Functional Site-Directed Fluorometry in Native Cells to Study Skeletal Muscle Excitability

CaV1.1, a member of the voltage-gated ion channels, has four distinct voltage sensors. Evidence suggests that some voltage sensors contribute more to ryanodine receptor activation or calcium current. We aim to be able to identify the precise role of each voltage sensor in excitation-contraction coupling and calcium channel activation.

Excitation-contraction coupling has been studied since the early 50s, yet the molecular detail of how this process occur are still unknown. Recent advance in cyro-electron microscopic structure of the channel, the characterization of novel CaV1.1 accessory protein, the discovery of channel alternative splicing variant, and the identification of disease-causing mutation have reignited the interest in this field. Many techniques are used in our field, from classical electrophysiology and molecular biology to more novel techniques such as cryo-electron microscopy, molecular dynamic simulation, targeted protein degradation, and functional site-directed fluorometry as well as engineered cells or animal models.

Currently, the fuel faces several experimental challenges. In a skeletal muscle, proper trafficking and communication between CaV1.1 and RyR1, along with many regulatory proteins, is crucial to support excitation-contraction coupling. The methods to directly study these protein-protein interactions between CaV1.1 and RyR1 are missing or incomplete.

The laboratory of Dr.Martin Schneider has been working on excitation-contraction coupling for decades, characterizing voltage-sensing mechanisms in CaV1.1, calcium release, and localized calcium-release events, known as calcium sparks. Recently, our laboratory has been implementing new optical techniques to investigate various steps of excitation-contraction coupling and voltage sensor motion in functioning adult muscle cells. While this has been done previously in a heterologous expression system, our protocol now allows tracking conformational changes in CaV1.1 voltage sensors during a propagated action potential in his native environment.

Our new technique will allow us to investigate the precise movement of the voltage sensor needed for excitation-contraction coupling. We want to know which charge residue in each S4 are critical for its function, or exactly each S4 translocate, and all that's translocation is linked to CaV1.1 opening or ryanodine receptor activation.